A tau class glutathione-S-transferase (OsGSTU5) confers tolerance against arsenic toxicity in rice by accumulating more arsenic in root

Arsenic transport, detoxification, and recent technologies for mitigation: A systemic review

Arsenic (As) is an acute toxic metalloid that affects plant growth and development. As is found in the environment in organic and inorganic forms, but arsenite As(III) and arsenate As(V) are the most prevalent forms that negatively impact the plants. Roots exposed to As can easily absorb it mainly through transporters that carry vital mineral nutrients. As reach the food chain via crops irrigated with As-polluted water and exerts a negative impact. Even at low levels, As exposure disrupts the regular functioning of plants by generating a high level of reactive oxygen species (ROS) results into oxidative damage, and disruption of redox system. Plants have built-in defence mechanisms to combat this oxidative damage. The development of a food crop with lower As levels is dependent upon understanding the molecular process of As detoxification in plants, which will help reduce the consumption of As-contaminated food. Numerous genes in plants that may provide tolerance under hazardous conditions have been examined using genetic engineering techniques. The suppression of genes by RNA interference (RNAi) and CRISPR-Cas 9 (CRISPR associated protein 9) technology revealed an intriguing approach for developing a crop that has minimal As levels in consumable portions. This study aims to present current information on the biochemical and molecular networks associated with As uptake, as well as recent advances in the field of As mitigation using exogenous salicylic acid (SA), Serendipita indica and biotechnological tools in terms of generating As-tolerant plants with low As accumulation.

Cr(VI) behaves differently than Cr(III) in the uptake, translocation and detoxification in rice roots

Excessive accumulation of chromium (Cr) causes severe damage to both physiological and biochemical processes and consequently growth repression in plants. Hexavalent chromium [Cr(VI)]-elicited alterations in plants have been widely elucidated at either physiological or molecular level, whereas little is known about trivalent chromium [Cr(III)]. Here, we found that both Cr(III) and Cr(VI) significantly inhibited root growth in rice plants. However, rice plants under Cr(VI) showed significantly less inhibition in root growth than those under Cr(III) at low levels, which might be attributed to the different hormetic effects of Cr(III) and Cr(VI) on rice plants. It was unexpected that Cr(III) could be actively taken up by rice roots similarly to Cr(VI); whereas they exhibited different kinetic uptake patterns. Furthermore, root-to-shoot Cr translocation under Cr(VI) was much lower than that under Cr(III). These results indicate that the uptake, translocation, and toxicity of Cr(III) differed greatly from those of Cr(VI). Transcriptome profiling of rice roots revealed that a series of gene families involved in detoxification, including ATP-binding cassette (ABC) transporters, multidrug and toxic compound extrusion proteins (MATEs), and Tau class glutathione S-transferases (GSTUs), were significantly associated with Cr accumulation and detoxification in rice roots. In addition, much more members of these gene families were upregulated by Cr(VI) compared to Cr(III), suggesting their vital roles in Cr uptake, translocation, and detoxification, especially under Cr(VI) stress. Further comparison of gstu9 and gstu10/50 mutants with their wild type confirmed that GSTUs play complex roles in the intracellular Cr transport and redox homeostasis during Cr(III) or Cr(VI) stress. Taken together, our findings provides new insights into the differential behaviors of Cr(III) and Cr(VI) in rice roots, as well as new candidate genes such as OsABCs and OsGSTUs, to further elucidate the mechanisms of the uptake, translocation, and detoxification of Cr(III) and Cr(VI).

Effects of Exogenous Application of Methyl Jasmonate and Salicylic Acid on the Physiological and Molecular Response of 'Dusa' Avocado to Rosellinia necatrix

Methyl jasmonate (MeJA) and salicylic acid (SA) are important in mediating plant responses to abiotic and biotic stresses. MeJA and SA can act as elicitors by triggering plant defense responses similar to those induced by pathogens and may even provide long-term protection against them. Thus, exogenous application of MeJA and SA could protect susceptible avocado plants against white root rot (WRR) disease caused by the necrotrophic fungus Rosellinia necatrix, one of the main diseases affecting avocado orchards. This work evaluates the effects of MeJA or SA on the physiological and molecular response of susceptible 'Dusa' avocado rootstock and their ability to provide some protection against WRR. The application of MeJA and SA in avocado increased photoprotective mechanisms (nonphotochemical chlorophyll fluorescence quenching) and upregulated the glutathione S-transferase, suggesting the triggering of mechanisms closely related to oxidative stress relief and reactive oxygen species scavenging. In contrast to SA, MeJA's effects were more pronounced at the morphoanatomical level, including functional traits such as high leaf mass area, high stomatal density, and high root/shoot ratio, closely related to strategies to cope with water scarcity and WRR disease. Moreover, MeJA upregulated a greater number of defense-related genes than SA, including a glu protease inhibitor, a key gene in avocado defense against R. necatrix. The overall effects of MeJA increased 'Dusa' avocado tolerance to R. necatrix by inducing a primed state that delayed WRR disease symptoms. These findings point toward the use of MeJA application as an environmentally friendly strategy to mitigate the impact of this disease on susceptible avocado orchards.

Targeting OsNIP3;1 via CRISPR/Cas9: A strategy for minimizing arsenic accumulation and boosting rice resilience

Arsenic (As) contamination in rice poses a significant threat to human health due to its toxicity and widespread consumption. Identifying and manipulating key genes governing As accumulation in rice is crucial for reducing this threat. The large NIP gene family of aquaporins in rice presents a promising target due to functional redundancy, potentially allowing for gene manipulation without compromising plant growth. This study aimed to utilize genome editing to generate knock-out (KO) lines of genes of NIP family (OsLsi1, OsNIP3;1) and an anion transporter family (OsLsi2), in order to assess their impact on As accumulation and stress tolerance in rice. KO lines were created using CRISPR/Cas9 technology, and the As accumulation patterns, physiological performance, and grain yield were compared against wild-type (WT) under As-treated conditions. KO lines exhibited significantly reduced As accumulation in grain compared to WT. Notably, Osnip3;1 KO line displayed reduced As in xylem sap (71-74%) and grain (32-46%) upon treatment. Additionally, these lines demonstrated improved silicon (23%) uptake, photosynthetic pigment concentrations (Chl a: 77%; Chl b: 79%, Total Chl: 79% & Carotenoid: 49%) overall physiological and agronomical performance under As stress compared to WT. This study successfully utilized genome editing for the first time to identify OsNIP3;1 as a potential target for manipulating As accumulation in rice without compromising grain yield or plant vigor.

Unveiling the molecular mechanisms of arsenic tolerance and resilience in the primitive bryophyte Marchantia polymorpha L

This study addresses the pressing issue of high arsenic (As) contaminations, which poses a severe threat to various life forms in our ecosystem. Despite this prevailing concern, all organisms have developed some techniques to mitigate the toxic effects of As. Certain plants, such as bryophytes, the earliest land plants, exhibit remarkable tolerance to wide range of harsh environmental conditions, due to their inherent competence. In this study, bryophytes collected from West Bengal, India, across varying contamination levels were investigated for their As tolerance capabilities. Assessment of As accumulation potential and antioxidant defense efficiency, including SOD, CAT, APX, GPX etc. revealed Marchantia polymorpha as the most tolerant species. It exhibited highest As accumulation, antioxidative proficiency, and minimal damage. Transcriptomic analysis of M. polymorpha exposed to 40 μM As(III) for 24 and 48 h identified several early responsive differentially expressing genes (DEGs) associated with As tolerance. These includes GSTs, GRXs, Hsp20s, SULTR1;2, ABCC2 etc., indicating a mechanism involving vacuolar sequestration. Interestingly, one As(III) efflux-transporter ACR3, an extrusion pump, known to combat As toxicity was found to be differentially expressed compared to control. The SEM-EDX analysis, further elucidated the operation of As extrusion mechanism, which contributes added As resilience in M. polymorpha. Yeast complementation assay using Δacr3 yeast cells, showed increased tolerance towards As(III), compared to the mutant cells, indicating As tolerant phenotype. Overall, these findings significantly enhance our understanding of As tolerance mechanisms in bryophytes. This can pave the way for the development of genetically engineered plants with heightened As tolerance and the creation of improved plant varieties.

Metagenomic and biochemical analyses reveal the potential of silicon to alleviate arsenic toxicity in rice (Oryza sativa L.)

Arsenic (As) pollution in agricultural systems poses a serious threat to crop productivity and food safety. Silicon (Si) has been reported to mitigate toxic effects of heavy metals in plants. However, the mechanisms behind Si-mediated alleviation of As toxicity in rice (Oryza sativa L.) remain poorly understood. Here, we performed metagenomic and biochemical analyses to investigate the potential of Si in alleviating As toxicity to rice plants. As exposure reduced plant growth, chlorophyll contents, antioxidant enzyme levels and soil enzymes activity, while increasing reactive oxygen species (ROS) activity and inducing alterations in the rhizosphere microbiome of rice seedlings. Silicon amendments enhanced rice growth (24%), chlorophyll a (25%), and chlorophyll b (26.7%), indicating enhanced photosynthetic capacity. Si amendments also led to the upregulation of antioxidant enzymes viz., superoxide dismutase (15.4%), and peroxidase (15.6%), resulting in reduced ROS activity and oxidative stress compared to the As-treated control. Furthermore, Si treatment reduced uptake and translocation of As in rice plants, as evidenced by the analysis of elemental contents. Microscopic examination of leaf and root ultrastructure showed that Si mitigated As-induced cellular damage and maintained normal morphology. Metagenomic analysis of the rice rhizosphere microbiome revealed that Si application modulated composition and diversity of microbial communities e.g., Proteobacteria, Actinobacteria, and Firmicutes. Additionally, Si amendments upregulated the relative expression levels of OsGSH, OsPCs, OsNIP1;1 and OsNIP3;3 genes, while the expression levels of the OsLis1 and OsLis2 genes were significantly downregulated compared with As-treated rice plants. Overall, these findings contribute to our understanding of Si-mediated plant resilience to As stress and offer potential strategies for sustainable agriculture in As-contaminated regions.

The Molecular Mechanism of the Response of Rice to Arsenic Stress and Effective Strategies to Reduce the Accumulation of Arsenic in Grain

Rice (Oryza sativa L.) is the staple food for more than 50% of the world's population. Owing to its growth characteristics, rice has more than 10-fold the ability to enrich the carcinogen arsenic (As) than other crops, which seriously affects world food security. The consumption of rice is one of the primary ways for humans to intake As, and it endangers human health. Effective measures to control As pollution need to be studied and promoted. Currently, there have been many studies on reducing the accumulation of As in rice. They are generally divided into agronomic practices and biotechnological approaches, but simultaneously, the problem of using the same measures to obtain the opposite results may be due to the different species of As or soil environments. There is a lack of systematic discussion on measures to reduce As in rice based on its mechanism of action. Therefore, an in-depth understanding of the molecular mechanism of the accumulation of As in rice could result in accurate measures to reduce the content of As based on local conditions. Different species of As have different toxicity and metabolic pathways. This review comprehensively summarizes and reviews the molecular mechanisms of toxicity, absorption, transport and redistribution of different species of As in rice in recent years, and the agronomic measures to effectively reduce the accumulation of As in rice and the genetic resources that can be used to breed for rice that only accumulates low levels of As. The goal of this review is to provide theoretical support for the prevention and control of As pollution in rice, facilitate the creation of new types of germplasm aiming to develop without arsenic accumulation or within an acceptable limit to prevent the health consequences associated with heavy metal As as described here.

Translocation, enzymatic reduction and toxicity of dimethylarsenate in rice

Dimethylarsenate [DMAs(V)] can be produced by some soil microorganisms through methylation of inorganic arsenic (As), especially in anoxic paddy soils. DMAs(V) is more phytotoxic than inorganic As and can cause the physiological disorder straighthead disease in rice. Rice cultivars vary widely in the resistance to DMAs(V), but the mechanism remains elusive. Here, we investigated the differences in DMAs(V) uptake, translocation, and reduction to dimethylarsenite [DMAs(III)], as well as the effects on the metabolome, between two rice cultivars Mars and Zhe733. We found that Mars was 11-times more resistant to DMAs(V) than Zhe733. Mars accumulated more DMAs(V) in the roots, whereas Zhe733 translocated more DMAs(V) to the shoots and reduced more DMAs(V) to DMAs(III). DMAs(III) was more toxic than DMAs(V). Using heterologous expression and in vitro enzyme assays, we showed that the glutathione-S-transferases OsGSTU17 and OsGSTU50 were able to reduce DMAs(V) to DMAs(III). The expression levels of OsGSTU17 and OsGSTU50 were higher in the shoot of Zhe733 compared to Mars. Metabolomic analysis in rice shoots showed that glutathione (GSH) metabolism was perturbed by DMAs(V) toxicity in Zhe733. Application of exogenous GSH significantly alleviated the toxicity of DMAs(V) in Zhe733. Taken together, the results suggest that Mars is more resistant to DMAs(V) than Zhe733 because of a lower root-to-shoot translocation and a smaller capacity to reduce DMAs(V) to DMAs(III).

Potentilla sericea stress-responsive spermine synthase PsSPMS enhances cadmium tolerance in Arabidopsis thaliana

Potentilla sericea is resistant and tolerates rough management. It is an excellent garden groundcover for ecological restoration and soil consolidation for slope protection. Polyamines have functions such as promoting tissue growth and physiological resistance, while spermine synthase catalyzes the production of spermine. The PsSPMS gene from Potentilla sericea was cloned and transformed into Arabidopsis thaliana to study the response of transgenic Arabidopsis thaliana to cadmium stress. The results showed that the contents of spermidine, spermine as well as glutathione were higher in PsSPMS overexpressing Arabidopsis thaliana than the control, while the contents of putrescine were less than the control. Net photosynthetic rate, stomatal conductance, chlorophyll content, water use efficiency, electron transfer rate, PSII-related parameters, proline content, superoxide dismutase, and glutathione reductase activities were higher in PsSPMS overexpressing Arabidopsis thaliana than the control, while malondialdehyde, superoxide anion, and hydrogen peroxide contents were lower than the control. Correlation analysis showed significant differences between the indicators (P < 0.05 and P < 0.01). Expression of AtSPMS, AtSPD3, AtGSH2 and AtGR in transgenic Arabidopsis thaliana was higher than that of the control. Therefore, this study provides a genetic reference for the cultivation of cadmium-tolerant plants through genetic engineering and lays the foundation for further research on cadmium-tolerant Potentilla sericea.

Isolation and characterization of glutathione S-transferase genes and their transcripts in Saccharina japonica (Laminariales, Phaeophyceae) during development and under abiotic stress

BACKGROUND

Glutathione S-transferase (GST) is a crucial enzyme for metabolism, detoxification, and stress resistance in organisms. Many GSTs have been identified in seaweeds, but the isolation and functional analysis of GSTs in Saccharina japonica have not been completed.

RESULT

In this study, a total of 32 SjGST genes, localized on 10 scaffolds and 6 contigs, were identified and categorized into three groups. Most of these SjGSTs were presumed to be distributed in the cytoplasm. Tandem duplication had a significant influence on the expansion of the SjGST gene family. Functional analysis of cis-acting elements in the promoter regions demonstrated that SjGSTs enhance the stress resistance of the kelp. Quantitative real-time PCR tests confirmed that SjGSTs positively influence S. japonica sporophytes under stress from low salinity, drought, and high temperature. Recombinant yeast tests further affirmed the role of SjGSTs in stress resistance; SjGSTs improved the growth rate of recombinant yeast under 1.5 M NaCl or 8 mM H2O2. Analysis of biochemical parameters indicated that the optimum temperatures for SjGST20 and SjGST22 were 20 °C, and the optimum pH values were 7.0 and 8.0 for SjGST20 and SjGST22, respectively. The Km values for the substrate 1-chloro-2,4-dinitrobenzene (CDNB) were 2.706 mM and 0.674 mM and were 6.146 mM and 3.559 mM for the substrate glutathione (GSH) for SjGST20 and SjGST22, respectively.

CONCLUSION

SjGSTs are important stress resistant genes in S. japonica. This research results will enhance our understanding the function of GSTs in brown seaweeds, and explained its functional roles in stress resistance in marine environments.

The protective role of tetraploidy and nanoparticles in arsenic-stressed rice: Evidence from RNA sequencing, ultrastructural and physiological studies

Genome doubling in plants induces physiological and molecular changes to withstand environmental stress. Diploid rice (D-2x) and its tetraploid (T-4x) plants were treated with 25 μM Arsenic (As) and 15 mg L-1 TiO2 nanoparticles (NPs), and results indicated decreased growth and photosynthetic activity with high accumulation of reactive oxygen species (ROS) due to the As-toxicity in rice lines, significantly in D-2x rice plants. The treatment of As-contaminated rice with TiO2 NPs resulted in increased root length (8.17%) and chlorophyll AB (13.28%) and decreased electrolyte leakage (21.76%) and H2O2 (17.65%) contents than its counterpart diploid rice. Moreover, TiO2 NPs improved the activity of peroxidase, catalase, glutathione, and superoxide dismutase and reduced lipid peroxidation due to lower ROS production in D-2x and T-4x under As toxicity. Transcriptome analysis revealed abrupt changes in the expression levels of key signaling heat shock proteins, tubulin, aquaporins, As, and metal transporters under As toxicity in T-4x and D-2x lines. The KEGG and GO studies highlighted the striking distinctions between rice lines under As-stress in glutathione metabolism, H2O2 catabolic process, MAPK signaling pathway, and carotenoid biosynthesis terms, revealing consistency between physiological and molecular results. Root cells from D-2x rice were significantly more distorted by As poisoning than those from 4x rice, and cell organelles, such as mitochondria and endoplasmic reticulum, were changed or deformed. These findings proved the superiority of tetraploid rice lines over their diploid counterpart in coping with As-stress.

OsGSTU17, a Tau Class Glutathione S-Transferase Gene, Positively Regulates Drought Stress Tolerance in Oryza sativa

As a great threat to the normal growth of rice, drought not only restricts the growth of rice, but also affects its yield. Glutathione S-transferases (GSTs) have antioxidant and detoxification functions. In rice, GSTs can not only effectively cope with biological stress, but also play a defense role against abiotic stress. In this study, we selected OsGSTU17, a member gene that was induced by drought, to explore the role of GSTs and analyze their physiological mechanisms that are involved in rice drought tolerance. With the CRISPR/Cas9 knockout system techniques, we obtained two independent mutant lines of osgstu17. After 14 days of drought stress treatment, and then re-supply of the water for 10 days, the survival rate of the osgstu17 mutant lines was significantly reduced compared to the wild-type (WT). Similarly, with the 10% (w/v) PEG6000 hydroponics experiment at the seedling stage, we also found that compared with the WT, the shoot and root biomass of osgstu17 mutant lines decreased significantly. In addition, both the content of the MDA and H2O2, which are toxic to plants, increased in the osgtu17 mutant lines. On the other hand, chlorophyll and proline decreased by about 20%. The activity of catalase and superoxide dismutase, which react with peroxides, also decreased by about 20%. Under drought conditions, compared with the WT, the expressions of the drought stress-related genes OsNAC10, OsDREB2A, OsAP37, OsP5CS1, OsRAB16C, OsPOX1, OsCATA, and OsCATB in the osgtu17 mutant lines were significantly decreased. Finally, we concluded that knocking out OsGSTU17 significantly reduced the drought tolerance of rice; OsGSTU17 could be used as a candidate gene for rice drought-tolerant cultivation. However, the molecular mechanism of OsGSTU17 involved in rice drought resistance needs to be further studied.

Differential effects of arsenite and arsenate on rice (Oryza sativa) plants differing in glutathione S-transferase gene expression

Contamination of paddy soils with arsenic (As) can cause phytotoxicity in rice and increase the accumulation of arsenic in grains. The uptake and accumulation of As in rice depends on the different As species present in the soil. Plants detoxify As by conjugating and sequestering xenobiotic compounds into vacuoles using various enzymes. However, the severity of damage induced by arsenite (As(III)) and arsenate (As(V)), as well as the roles of glutathione S-transferase in detoxifying these As species in rice, are not fully understood. In this study, we developed plant materials overexpressing a glutathione S-transferase gene OsGSTU40 under the control of the maize UBIL promoter. Through systematic investigations of both wild-type Nipponbare (Oryza sativa L., ssp. japonica) and OsGSTU40 overexpression lines under chronic or acute stress of As, we aimed to understand the toxic effects of both As(III) and As(V) on rice plants at the vegetative growth stage. We hypothesized that (i) As(III) and As(V) have different toxic effects on rice plants and (ii) OsGSTU40 played positive roles in As toxicity tolerance. Our results showed that As(III) was more detrimental to plant growth than As(V) in terms of plant growth, biomass, and lipid peroxidation in both chronic and acute exposure. Furthermore, overexpression of OsGSTU40 led to better plant growth even though uptake of As(V), but not As(III), into shoots was enhanced in transgenic plants. In acute As(III) stress, transgenic plants exhibited a lower level of lipid peroxidation than wild-type plants. The element composition of plants was dominated by the different As stress treatments rather than by the genotype, while the As concentration was negatively correlated with phosphorus and silicon. Overall, our findings suggest that As(III) is more toxic to plants than As(V) and that glutathione S-transferase OsGSTU40 differentially affects plant reactions and tolerance to different species of arsenic.

Regulatory Mechanisms Underlying Arsenic Uptake, Transport, and Detoxification in Rice

Arsenic (As) is a metalloid environmental pollutant ubiquitous in nature that causes chronic and irreversible poisoning to humans through its bioaccumulation in the trophic chain. Rice, the staple food crop for 350 million people worldwide, accumulates As more easily compared to other cereal crops due to its growth characteristics. Therefore, an in-depth understanding of the molecular regulatory mechanisms underlying As uptake, transport, and detoxification in rice is of great significance to solving the issue of As bioaccumulation in rice, improving its quality and safety and protecting human health. This review summarizes recent studies on the molecular mechanisms of As toxicity, uptake, transport, redistribution, regulation, and detoxification in rice. It aims to provide novel insights and approaches for preventing and controlling As bioaccumulation in rice plants, especially reducing As accumulation in rice grains.

Functional characterization of rice metallothionein OsMT-I-Id: Insights into metal binding and heavy metal tolerance mechanisms

Metallothioneins (MTs) are cysteine-rich proteins known for their strong metal-binding capabilities, making them effective in detoxifying heavy metals (HMs). This study focuses on characterizing the functional properties of OsMT-I-Id, a type-I Metallothionein found in rice. Using a HM-responsive yeast cup1Δ (DTY4), ycf1∆ (for cadmium), and acr3∆ mutants (for trivalent arsenic), we assessed the impact of OsMT-I-Id on metal accumulation and cellular resilience. Our results demonstrated that yeast cells expressing OsMT-I-Id showed increased tolerance and accumulated higher levels of copper (Cu), arsenic (As), and cadmium (Cd), compared to control cells. This can be attributed to the protein's ability to chelate and bind HMs. Site-directed mutagenesis was employed to investigate the specific contributions of cysteine residues. The study revealed that yeast cells with a mutated C-domain displayed heightened HM sensitivity, while cells with a mutated N-domain exhibited reduced sensitivity. This underscores the critical role of C-cysteine-rich domains in metal binding and tolerance of type-I rice MTs. Furthermore, the study identified the significance of the 12th cysteine position at the N-domain and the 68th and 72nd cysteine positions at the C-domain in influencing OsMT-I-Id metal-binding capacity. This research provides novel insights into the structure-function relationship and metal binding properties of type-I plant MTs.

Negative Impacts of Arsenic on Plants and Mitigation Strategies

Arsenic (As) is a metalloid prevalent mainly in soil and water. The presence of As above permissible levels becomes toxic and detrimental to living organisms, therefore, making it a significant global concern. Humans can absorb As through drinking polluted water and consuming As-contaminated food material grown in soil having As problems. Since human beings are mobile organisms, they can use clean uncontaminated water and food found through various channels or switch from an As-contaminated area to a clean area; but plants are sessile and obtain As along with essential minerals and water through roots that make them more susceptible to arsenic poisoning and consequent stress. Arsenic and phosphorus have many similarities in terms of their physical and chemical characteristics, and they commonly compete to cause physiological anomalies in biological systems that contribute to further stress. Initial indicators of arsenic's propensity to induce toxicity in plants are a decrease in yield and a loss in plant biomass. This is accompanied by considerable physiological alterations; including instant oxidative surge; followed by essential biomolecule oxidation. These variables ultimately result in cell permeability and an electrolyte imbalance. In addition, arsenic disturbs the nucleic acids, the transcription process, and the essential enzymes engaged with the plant system's primary metabolic pathways. To lessen As absorption by plants, a variety of mitigation strategies have been proposed which include agronomic practices, plant breeding, genetic manipulation, computer-aided modeling, biochemical techniques, and the altering of human approaches regarding consumption and pollution, and in these ways, increased awareness may be generated. These mitigation strategies will further help in ensuring good health, food security, and environmental sustainability. This article summarises the nature of the impact of arsenic on plants, the physio-biochemical mechanisms evolved to cope with As stress, and the mitigation measures that can be employed to eliminate the negative effects of As.

Phytoremediation potential of Solanum viarum Dunal and functional aspects of their capitate glandular trichomes in lead, cadmium, and zinc detoxification

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg^-1 DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg^-1DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM-EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Phytoremediation technologies and their mechanism for removal of heavy metal from contaminated soil: An approach for a sustainable environment

The contamination of soils with heavy metals and its associated hazardous effects are a thrust area of today's research. Rapid industrialization, emissions from automobiles, agricultural inputs, improper disposal of waste, etc., are the major causes of soil contamination with heavy metals. These contaminants not only contaminate soil but also groundwater, reducing agricultural land and hence food quality. These contaminants enter the food chain and have a severe effect on human health. It is important to remove these contaminants from the soil. Various economic and ecological strategies are required to restore the soils contaminated with heavy metals. Phytoremediation is an emerging technology that is non-invasive, cost-effective, and aesthetically pleasing. Many metal-binding proteins (MBPs) of the plants are significantly involved in the phytoremediation of heavy metals; the MBPs include metallothioneins; phytochelatins; metalloenzymes; metal-activated enzymes; and many metal storage proteins, carrier proteins, and channel proteins. Plants are genetically modified to enhance their phytoremediation capacity. In Arabidopsis, the expression of the mercuric ion-binding protein in Bacillus megaterium improves the metal accumulation capacity. The phytoremediation efficiency of plants is also enhanced when assisted with microorganisms, biochar, and/or chemicals. Removing heavy metals from agricultural land without challenging food security is almost impossible. As a result, crop selections with the ability to sequester heavy metals and provide food security are in high demand. This paper summarizes the role of plant proteins and plant-microbe interaction in remediating soils contaminated with heavy metals. Biotechnological approaches or genetic engineering can also be used to tackle the problem of heavy metal contamination.

Arsenic-Induced Oxidative Stress and Antioxidant Defense in Plants

The non-essential metalloid arsenic (As) is widely distributed in soil and underground water of many countries. Arsenic contamination is a concern because it creates threat to food security in terms of crop productivity and food safety. Plants exposed to As show morpho-physiological, growth and developmental disorder which altogether result in loss of productivity. At physiological level, As-induced altered biochemistry in chloroplast, mitochondria, peroxisome, endoplasmic reticulum, cell wall, plasma membrane causes reactive oxygen species (ROS) overgeneration which damage cell through disintegrating the structure of lipids, proteins, and DNA. Therefore, plants tolerance to ROS-induced oxidative stress is a vital strategy for enhancing As tolerance in plants. Plants having enhanced antioxidant defense system show greater tolerance to As toxicity. Depending upon plant diversity (As hyperaccumulator/non-hyperaccumulator or As tolerant/susceptible) the mechanisms of As accumulation, absorption or toxicity response may differ. There can be various crop management practices such as exogenous application of nutrients, hormones, antioxidants, osmolytes, signaling molecules, different chelating agents, microbial inoculants, organic amendments etc. can be effective against As toxicity in plants. There is information gap in understanding the mechanism of As-induced response (damage or tolerance response) in plants. This review presents the mechanism of As uptake and accumulation in plants, physiological responses under As stress, As-induced ROS generation and antioxidant defense system response, various approaches for enhancing As tolerance in plants from the available literatures which will make understanding the to date knowledge, knowledge gap and future guideline to be worked out for the development of As tolerant plant cultivars.